59 lines
4.0 KiB
Markdown
59 lines
4.0 KiB
Markdown
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# About Kohana Cache
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[Kohana_Cache] provides a common interface to a variety of caching engines. [Kohana_Cache_Tagging] is
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supported where available natively to the cache system. Kohana Cache supports multiple
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instances of cache engines through a grouped singleton pattern.
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## Supported cache engines
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* APC ([Cache_Apc])
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* eAccelerator ([Cache_Eaccelerator])
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* File ([Cache_File])
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* Memcached ([Cache_Memcache])
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* Memcached-tags ([Cache_Memcachetag])
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* SQLite ([Cache_Sqlite])
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* Xcache ([Cache_Xcache])
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## Introduction to caching
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Caching should be implemented with consideration. Generally, caching the result of resources
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is faster than reprocessing them. Choosing what, how and when to cache is vital. [PHP APC](http://php.net/manual/en/book.apc.php) is one of the fastest caching systems available, closely followed by [Memcached](http://memcached.org/). [SQLite](http://www.sqlite.org/) and File caching are two of the slowest cache methods, however usually faster than reprocessing
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a complex set of instructions.
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Caching engines that use memory are considerably faster than file based alternatives. But
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memory is limited whereas disk space is plentiful. If caching large datasets, such as large database result sets, it is best to use file caching.
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[!!] Cache drivers require the relevant PHP extensions to be installed. APC, eAccelerator, Memecached and Xcache all require non-standard PHP extensions.
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## What the Kohana Cache module does (and does not do)
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This module provides a simple abstracted interface to a wide selection of popular PHP cache engines. The caching API provides the basic caching methods implemented across all solutions, memory, network or disk based. Basic key / value storing is supported by all drivers, with additional tagging and garbage collection support where implemented or required.
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_Kohana Cache_ does not provide HTTP style caching for clients (web browsers) and/or proxies (_Varnish_, _Squid_). There are other Kohana modules that provide this functionality.
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## Choosing a cache provider
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Getting and setting values to cache is very simple when using the _Kohana Cache_ interface. The hardest choice is choosing which cache engine to use. When choosing a caching engine, the following criteria must be considered:
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1. __Does the cache need to be distributed?__
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This is an important consideration as it will severely limit the options available to solutions such as Memcache when a distributed solution is required.
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2. __Does the cache need to be fast?__
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In almost all cases retrieving data from a cache is faster than execution. However generally memory based caching is considerably faster than disk based caching (see table below).
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3. __How much cache is required?__
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Cache is not endless, and memory based caches are subject to a considerably more limited storage resource.
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Driver | Storage | Speed | Tags | Distributed | Automatic Garbage Collection | Notes
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---------------- | ------------ | --------- | -------- | ----------- | ---------------------------- | -----------------------
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APC | __Memory__ | Excellent | No | No | Yes | Widely available PHP opcode caching solution, improves php execution performance
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eAccelerator | __Memory__ | Excellent | No | No | Yes | Limited support and no longer developed. Included for legacy systems
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File | __Disk__ | Poor | No | No | No | Marginally faster than execution
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Memcache (tag) | __Memory__ | Good | No (yes) | Yes | Yes | Generally fast distributed solution, but has a speed hit due to variable network latency
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Sqlite | __Disk__ | Poor | Yes | No | No | Marginally faster than execution
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Xcache | __Memory__ | Excellent | Yes | No | Yes | Very fast memory solution and alternative to APC
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It is possible to have hybrid cache solutions that use a combination of the engines above in different contexts. This is supported with _Kohana Cache_ as well.
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## Minimum requirements
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* Kohana 3.0.4
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* PHP 5.2.4 or greater
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